(1) Field of the Invention
The present invention relates to a process for producing a barrel of a telescopic universal transmission joint, especially for motor vehicles.
The present invention also relates to a tool for producing such a barrel.
The present invention likewise relates to a telescopic universal transmission joint comprising such a barrel, especially for motor vehicles.
(2) State of the Prior Art
FR-A-2,607,883 makes known a homokinetic transmission joint comprising an internal member, also called a "tripod", equipped with three arms arranged substantially radially in relation to its axis and each partially surrounded by two roller segments. Radially outer faces of curved transverse profile of the roller segments are in longitudinal rolling and lateral oscillation contact with longitudinal tracks formed on the inner face of a barrel, which surrounds the internal member and which is connected to one of two shafts between which transmission is to be obtained.
The interposed members, each consisting, according to this document, of roller segments, transmit forces oriented tangentially between the arms of the internal member and the corresponding tracks of the barrel at a point on the tracks which is a function of the state of telescopic compression of the joint, of the angle between the axes of the internal member and the barrel, and of the position of the particular arm in relation to the plane in which these two axes are located. Instead of being roller segments, the interposed members can be blocks which slide along the tracks or composite members capable of rolling and sliding, as provided according to FR-A-2,622,653, or members of variable configuration, as described, for example, in FR-A-2,525,306. Conventionally, the internal member has three radial arms, which is why it is usually called a tripod, but this number is not mandatory, and internal members having, for example, two or four arms are possible.
The barrel is often closed on one side by a bottom, so as to form with this bottom what is called a "bowl" of a generally cylindrical shape.
The barrel is produced from a steel blank having a cylindrical outer surface and an inner surface in which the longitudinal tracks are machined. The barrel is generally the part of the joint involving the highest outlay because of its volume of material and the difficulty of machining the tracks with the accuracy and the surface state required on the inside of this part closed by the bottom.
Attempts have been made to carry out cold or semi-hot extrusion processes, but the surface quality, profile accuracy and correctness necessary for the tracks are insufficient to ensure that, in the production of large series, these joints have the expected high degree of comfort during operation under economically competitive conditions.
Moreover, each track has a length which is large in relation to its diameter, and therefore the grinding of the tracks involves too high an outlay.